Revert "[clang] - Simplify tools::SplitDebugName."

This reverts commit r347035 as it introduced assertion failures under
certain conditions. More information can be found here:
https://reviews.llvm.org/rL347035

llvm-svn: 347676
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 1af9935..d7797d9 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -817,7 +817,7 @@
   if (Args.hasArg(options::OPT_gsplit_dwarf) &&
       getToolChain().getTriple().isOSLinux())
     SplitDebugInfo(getToolChain(), C, *this, JA, Args, Output,
-                   SplitDebugName(Args, Output));
+                   SplitDebugName(Args, Inputs[0], Output));
 }
 
 namespace {